Method and apparatus for reducing image artifacts

ABSTRACT

A method and apparatus are provided for reducing motion related imaging artifacts. The method includes determining an internal motion for of two regions of the object, each region having a different level of motion, scanning the first region using a first scan protocol based on the motion, scanning a second region using a second different scan protocol based on the motion, and generating an image of the object based on the first and second regions.

BACKGROUND OF THE INVENTION

The invention relates generally to imaging systems, and moreparticularly, embodiments relate to an apparatus and method for reducingimage artifacts that are produced by movement of an object.

Multi-modality imaging systems exist that scan using differentmodalities, such as, for example, Computed Tomography (CT), MagneticResonance Imaging (MRI), Positron Emission Tomography (PET), and SinglePhoton Emission Computed Tomography (SPECT). During operation,conventional imaging systems may exhibit image quality that is affectedby motion of the object being imaged.

Motion of the object being imaged may degrade image quality, for examplein medical imaging. More specifically, image artifacts are produced bymovement of the object. Involuntary motion in mammals (e.g., people andanimals) encountered in medical imaging systems is a common source ofimage artifacts. The involuntary motion may lead to errors, such as whena physician is determining the size of a lesion, determining thelocation of the lesion, or quantifying the lesion.

To correct for motion related imaging artifacts, at least oneconventional imaging system utilizes a prior knowledge of areas thattypically exhibit motion. For example, when imaging a patient, themotion of the diaphragm may cause motion related artifacts to be presentin the image. One conventional method to compensate for diaphragm motionis to determine the location of the diaphragm and to use a priorknowledge of typical diaphragm movement to modify the scan acquisitionprotocol to compensate for the diaphragm motion. The patient is thenimaged using the modified scan acquisition protocol. The a prioriknowledge is typically based on the operator's knowledge of the quantityof expected diaphragm motion not on the actual movement of the specificpatient diaphragm being imaged. Specifically, the conventional motioncorrection method relies on the assumption that the movement of thediaphragm is approximately the same for each patient. However, diaphragmmotion varies from patient to patient. Another conventional method fordetermining motion utilizes an external sensor to detect motion. Forexample, the external sensor may sense the movement of the chest of apatient during the breathing cycle. However, the movement of the chestis generally different than the movement of the internal organs such asthe diaphragm, for example. As a result, the conventional methods maynot adequately determine the movement of internal organs and thereforemay not adequately compensate for motion related artifacts in the imageproduced.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method for reducing, in an images motion relatedimaging artifacts is provided. The method includes determining aninternal motion of two regions of the object, each region having adifferent level of motion, scanning the first region using a first scanprotocol based on the motion, scanning a second region using a seconddifferent scan protocol based on the motion, and generating an image ofthe object based on the first and second regions.

In another embodiment, a multi-modality imaging system is provided. Themulti-modality imaging system includes a first modality unit, a secondmodality unit, and a computer operationally coupled to the first andsecond modality units. The computer is programmed to determine aninternal motion for of two regions of the object, each region having adifferent level of motion, scan the first region using a first scanprotocol based on the motion, scan a second region using a seconddifferent scan protocol based on the motion, and generate an image ofthe object based on the first and second regions.

In a further embodiment, a computer readable medium is provided. Thecomputer readable medium is programmed to instruct a computer todetermine an internal motion for of two regions of the object, eachregion having a different level of motion, scan the first region using afirst scan protocol based on the motion, scan a second region using asecond different scan protocol based on the motion, and generate animage of the object based on the first and second regions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of an exemplary multi-modality imaging systemin accordance with an embodiment of the present invention.

FIG. 2 is a block schematic diagram of an exemplary imaging system thatmay be used with the multi-modality imaging system illustrated in FIG. 1in accordance with an embodiment of the present invention.

FIG. 3 is a block schematic diagram of another exemplary imaging systemthat may be used with the multi-modality imaging system illustrated inFIG. 1 in accordance with an embodiment of the present invention.

FIG. 4 is a flowchart illustrating an exemplary method for reducingartifacts in an image that result from motion of an object being imaged.

FIG. 5 is exemplary motion information generated using the systemillustrated in FIG. 1 in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofcertain embodiments of the present invention, will be better understoodwhen read in conjunction with the appended drawings. To the extent thatthe figures illustrate diagrams of the functional blocks of variousembodiments, the functional blocks are not necessarily indicative of thedivision between hardware circuitry. Thus, for example, one or more ofthe functional blocks (e.g., processors or memories) may be implementedin a single piece of hardware (e.g., a general purpose signal processoror a block of random access memory, hard disk, or the like). Similarly,the programs may be stand alone programs, may be incorporated assubroutines in an operating system, may be functions in an installedsoftware package, and the like. It should be understood that the variousembodiments are not limited to the arrangements and instrumentalityshown in the drawings.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising” or “having”an element or a plurality of elements having a particular property mayinclude additional elements not having that property.

Also as used herein, the phrase “reconstructing an image” is notintended to exclude embodiments of the present invention in which datarepresenting an image is generated but a viewable image is not.Therefore, as used herein the term “image” broadly refers to bothviewable images and data representing a viewable image. However, manyembodiments generate, or are configured to generate, at least oneviewable image.

Various embodiments of the invention provide a multi-modality imagingsystem 10 as shown in FIGS. 1 and 2. Multi-modality imaging system 10may include any type imaging system, for example, different types ofmedical imaging systems, such as a Positron Emission Tomography (PET)imaging system, a Single Photon Emission Computed Tomography (SPECT)imaging system, a Computed Tomography (CT) imaging system, an ultrasoundimaging system, a Magnetic Resonance Imaging (MRI) imaging system or anyother system capable or generating medical images. The variousembodiments are not limited to multi-modality medical imaging systems,but may be used on a single modality medical imaging system such as astand-alone PET imaging system, a stand-alone SPECT imaging system, or astand-alone MRI imaging system, for example. While, some of theembodiments are described herein with respect to a PET imaging systemhaving a stationary detector, it should be realized that the embodimentsdescribed herein may also be used with other types of PET imagingsystems. Other types of PET imaging systems may include, for example, aPET imaging system having a non-stationary detector or a Time-of-Flight(TOF) PET imaging system. Moreover, the various embodiments are notlimited to medical imaging systems for imaging human subjects, but mayinclude veterinary or non-medical systems for imaging non-human objectsetc.

Referring to FIG. 1, the multi-modality imaging system 10 includes afirst modality unit 12 and a second modality unit 13. The two modalityunits enable the multi-modality imaging system 10 to scan a patient orobject 16 in a first modality using the first modality unit 12 and toscan the object 16 in a second modality using the second modality unit13. The multi-modality imaging system 10 allows for multiple scans indifferent modalities to facilitate an increased diagnostic capabilityover single modality systems. In one embodiment, multi-modality imagingsystem 10 is a Computed Tomography/Positron Emission Tomography (CT/PET)imaging system 10, e.g. the first modality 12 is a CT imaging system andthe second modality 13 is a PET imaging system. The imaging system 10 isshown as including a gantry 18 that is associated with the firstmodality unit 12 and a gantry 20 that is associated with the secondmodality unit 13. During operation, the object 16 is positioned within acentral opening 22, defined through the imaging system 10, using, forexample, a motorized table 24.

The gantry 18 includes an x-ray source 26 that projects a beam of x-raystoward a detector array 28 on the opposite side of the gantry 18.Detector array 28 is formed by a plurality of detector rows (not shown)including a plurality of detector elements which together sense theprojected x-rays that pass through the object 16. Each detector elementproduces an electrical signal that represents the intensity of animpinging x-ray beam and hence allows estimation of the attenuation ofthe beam as it passes through the object 16. During a scan to acquirex-ray projection data, gantry 18 and the components mounted thereonrotate about a center of rotation.

FIG. 2 is a block schematic diagram of a PET imaging system that may beused with the multi-modality imaging system illustrated in FIG. 1 inaccordance with an embodiment of the present invention. In one exemplaryembodiment, the first modality unit 12 is a Computed Tomographic (CT)imaging system and the second modality 13 is the Positron EmissionTomography (PET) imaging system 14 illustrated in FIG. 2. The PETimaging system 14 includes a detector ring assembly 30 including aplurality of detector scintillators. Each scintillator may be coupled tomultiple photomultiplier tubes (PMTs) or other light sensors thatconvert the light from the scintillator assembly into an electricsignal. In addition to the scintillator-PMT combination, pixilatedsolid-state direct conversion detectors (e.g., CZT) may also be used togenerate electric signals from the impact of the photons.

The detector ring assembly 30 includes the central opening 22, in whichan object or patient, such as object 16 may be positioned, using, forexample, the motorized table 24 (shown in FIG. 1). The motorized table24 is aligned with the central axis of the detector ring assembly 30.During operation, the motorized table 24 moves the object 16 into thecentral opening 22 of the detector ring assembly 30 in response to oneor more commands received from an operator workstation 34. Morespecifically, a PET scanner controller 36 responds to the commandsreceived from the operator workstation 34 through a communication link38. Therefore, the scanning operation is controlled from the operatorworkstation 34 through PET scanner controller 36.

The workstation 34 may be embodied as a personal computer (PC) that ispositioned near the PET imaging system 14 and hard-wired to the PETscanner controller 36 via the communication link 38. The workstation 34may also be embodied as a portable computer such as a laptop computer ora hand-held computer that transmits information to the PET scannercontroller 36. In one embodiment, the communication link 38 may behardwired between the PET scanner controller 36 and the workstation 34.Optionally, the communication link 38 may be a wireless communicationlink that enables information to be transmitted to or from theworkstation to the PET scanner controller 36 wirelessly. In theexemplary embodiment, the workstation 34 controls real-time operation ofthe PET imaging system 14. The workstation 34 is also programmed toperform medical image diagnostic acquisition and reconstructionprocesses described herein.

The operator workstation 34 includes a central processing unit (CPU) orcomputer 40, a display 42 and an input device 44. As used herein, theterm “computer” may include any processor-based or microprocessor-basedsystem including systems using microcontrollers, reduced instruction setcomputers (RISC), application specific integrated circuits (ASICs),field programmable gate array (FPGAs), logic circuits, and any othercircuit or processor capable of executing the functions describedherein. The above examples are exemplary only, and are thus not intendedto limit in any way the definition and/or meaning of the term“computer”. In the exemplary embodiment, the computer 40 executes a setof instructions that are stored in one or more storage elements ormemories, in order to process input data. The storage elements may alsostore data or other information as desired or needed. The storageelement may be in the form of an information source or a physical memoryelement within the computer 40.

The set of instructions may include various commands that instruct thecomputer or processor 40 as a processing machine to perform specificoperations such as the methods and processes of the various embodimentsdescribed herein. The set of instructions may be in the form of asoftware program. As used herein, the terms “software” and “firmware”are interchangeable, and include any computer program stored in memoryfor execution by a computer, including RAM memory, ROM memory, EPROMmemory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The abovememory types are exemplary only, and are thus not limiting as to thetypes of memory usable for storage of a computer program.

The software may be in various forms such as system software orapplication software. Further, the software may be in the form of acollection of separate programs, a program module within a largerprogram or a portion of a program module. The software also may includemodular programming in the form of object-oriented programming. Theprocessing of input data by the processing machine may be in response touser commands, or in response to results of previous processing, or inresponse to a request made by another processing machine.

The CPU 40 connects to the communication link 38 and receives inputs,e.g., user commands, from the input device 44. The input device 44 maybe, for example, a keyboard, mouse, a touch-screen panel, and/or a voicerecognition system, etc. Through input device 44 and associated controlpanel switches, the operator can control the operation of the PETimaging system 14 and the positioning of the object 16 for a scan.Similarly, the operator can control the display of the resulting imageon the display 42 and can perform image-enhancement functions usingprograms executed by the workstation CPU 40.

During operation of one exemplary detector, when a photon collides witha scintillator on the detector ring assembly 30, the photon collisionproduces a scintilla on the scintillator. The scintillator produces ananalog signal that is transmitted on a communication link 46 when ascintillation event occurs. A set of acquisition circuits 48 is providedto receive these analog signals. The acquisition circuits 48 process theanalog signals to identify each valid event and provide a set of digitalnumbers or values indicative of the identified event. For example, thisinformation indicates when the event took place and the position of thescintillator that detected the event.

The digital signals are transmitted through a communication link, forexample, a cable, to a data acquisition controller 52. The dataacquisition controller 52 is adapted to determine a motion of at leastone region of interest within the object 16 based on the obtained imagedata set and modify the scan acquisition protocol based on thedetermined motion. The scan acquisition protocol is a set ofinstructions or scan acquisition parameters that control the scanningoperation of the object 16. The data acquisition controller 52 is alsoadapted to perform image reconstruction processes as described hereinand various other functions. In one embodiment, the data acquisitioncontroller 52 is positioned remotely from the workstation 34 andcommunicates with the workstation 34 and PET scanner controller 36 via acommunication link 54. Optionally, the data acquisition controller 52may be embedded within the workstation 34. For example, the dataacquisition controller 52 may be physically separate from the CPU 40 andused in conjunction with the CPU 40 to improve or enhance the imageprocessing speed. In another embodiment, the CPU 40 may perform all theprocessing functions performed by the data acquisition controller 52,e.g. the data acquisition controller 52 is embedded in the workstation34 such that CPU 40 performs the modification of the scan acquisitionprotocol based on the determined motion and image reconstructionprocesses performed by the data acquisition controller 52.

In one embodiment, the data acquisition controller 52 includes a dataacquisition processor 60 and an image reconstruction processor 62 thatare interconnected via a communication link 64. During operation, theacquisition circuits 48 transmit the digital signals to the dataacquisition processor 60. The data acquisition processor 60 thenperforms various image enhancing techniques on the digital signals andtransmits the enhanced or corrected digital signals to the imagereconstruction processor 62 as discussed in more detail below.

In the exemplary embodiment, the data acquisition processor 60 includesat least an acquisition CPU or computer 70. The data acquisitionprocessor 60 also includes an event locator circuit 72 and a coincidencedetector 74. The acquisition CPU 70 controls communications on aback-plane bus 76 and on the communication link 64. During operation,the data acquisition processor 60 periodically samples the digitalsignals produced by the acquisition circuits 48. The digital signalsproduced by the acquisition circuits 48 are transmitted to the eventlocator circuit 72. The event locator circuit 72 processes theinformation to identify each valid event and provides a set of digitalnumbers or values indicative of the identified event. For example, thisinformation indicates when the event took place and the position of thescintillator that detected the event. The events are also counted toform a record of the single channel events recorded by each detectorelement. An event data packet is communicated to the coincidencedetector 74 through the back-plane bus 76.

The coincidence detector 74 receives the event data packets from theevent locator circuit 72 and determines if any two of the detectedevents are in coincidence. Coincidence is determined by a number offactors. First, the time markers in each event data packet must bewithin a predetermined time period, for example, 12.5 nanoseconds, ofeach other. Second, the line-of-response (LOR) formed by a straight linejoining the two detectors that detect the coincidence event should passthrough the field of view in the PET imaging system 14. Events thatcannot be paired are discarded. Coincident event pairs are located andrecorded as a coincidence data packet by the coincidence detector 74 andthen communicated through the back-plane bus 76 to a motioncharacterization module 78. The output from the coincidence detector 74is referred to herein as an emission data set 80 or raw image data. Inone embodiment, the emission data set 80 may be stored in a memory 82that is located in the data acquisition processor 60. Optionally, theemission data set 80 may be stored in the workstation 34. The operationof the motion characterization module 78 is discussed in more detailbelow.

The motion corrected emission data set is then transmitted to asorter/histogrammer 128 to generate a data structure known as ahistogram. A histogram includes a large number of bins, where each bincorresponds to one or more unique pairs of detector scintillators in thePET scanner and motion state as determined by the motioncharacterization module 78. The histogrammer 210 may also take otherinformation into account such as detected energies and/or arrival times,e.g. in a Time of Flight PET scanner and/or for dynamic data. Because aPET scanner typically includes thousands of detector scintillators, thehistogram typically includes millions of bins. Each bin of the histogramalso stores a count value representing the number of coincidence eventsdetected by the pair of detector scintillators for that bin during thescan. At the end of the scan, the data in the histogram is used toreconstruct an image of the patient. The completed histogram containingall the data from the scan is commonly referred to as a “resulthistogram.” The term “histogrammer” generally refers to the componentsof the scanner, e.g., processor and memory, which carry out the functionof creating the histogram.

The image reconstruction processor 62 also includes a memory module 130,an image CPU 132, an array processor 134, and a communication bus 136.During operation, the sorter/histogrammer 128 counts all events in thebins of the histogram as discussed above. This data is organized in oneexemplary embodiment as a data array 138. The data array 138 is storedin the memory module 130. The communication bus 136 is linked to theback-plane bus 76 through the image CPU 132. The image CPU 132 controlscommunication through communication bus 136. The array processor 134 isalso connected to the communication bus 136. The array processor 134receives the data array 138 as an input and reconstructs images in theform of image arrays 140. Resulting image arrays 140 are then stored inmemory module 130. The images stored in the image array 140 arecommunicated by the image CPU 132 to the operator workstation 34.

FIG. 3 is a block schematic diagram of a Magnetic Resonance Imaging(MRI) system 15 that may be used with the multi-modality imaging systemillustrated in FIG. 1 in accordance with an embodiment of the presentinvention. In one exemplary embodiment, the first modality unit 12 is aComputed Tomographic (CT) imaging system and the second modality 13 isthe MRI imaging system 15 illustrated in FIG. 3. In the exemplaryembodiment, the MPI system 15 includes an electromagnet 102, pole pieces104, a controller 106, a main magnetic field control 108, a gradientcoil sub-system 110, a gradient field control 112, a memory 114, adisplay device 116, a transmit-receive (T-R) switch 120, a radiofrequency (RF) transmitter 122, a receiver 124 and an array of detectors126 (e.g., a cylindrical array of equally-spaced detectors).

In use of the MRI system 15, an object 16, such as a patient to beimaged, is placed in an opening 22 between pole pieces 104 on a suitablesupport (e.g., motorized table 24 shown in FIG. 1). The electromagnet102 produces a uniform and static main magnetic field B_(o) across theopening 22. The strength of the electromagnetic field in the opening 22and correspondingly in the object 16, is controlled by the controller106 via a main magnetic field control 108, which also controls a supplyof energizing current to the electromagnet 102.

The gradient coil sub-system 110, having one or more gradient coils, isprovided so that a magnetic gradient can be imposed on the magneticfield B_(o) in the opening 22 between pole pieces 104 in any one or moreof three orthogonal directions x, y, and z. Gradient coil sub-system 110is energized by gradient field control 112 and is also controlled by thecontroller 106.

The array 126, which may include a plurality of coils (e.g., resonantsurface coils), is arranged to simultaneously detect MR signals from theobject 16. The array 126 is selectably interconnected to one of the RFtransmitter 122 or receiver 124 by the T-R switch 120. The RFtransmitter 122 and T-R switch 120 are controlled by the controller 106such that RF field pulses or signals are generated by the RF transmitter122 and selectively applied to the object 16 for excitation of magneticresonance in the object 16. While the RF excitation pulses are beingapplied to the object 16, the T-R switch 120 also is actuated todecouple the receiver 124 from the array 126.

Following application of the RF pulses, the T-R switch 120 is againactuated to decouple the array 126 from the RF transmitter 122 and tocouple the array 126 to the receiver 124. The array 126 includesdetectors that operate to detect or sense the MR signals resulting fromthe excited nuclei in the object 16 and communicates the MR signals tothe receiver 124. These detected MR signals are in turn communicated tothe controller 106. The controller 106 includes a processor (e.g., imagereconstruction processor) that controls the processing of the MR signalsto produce signals representative of an image of the object 16. Theprocessed signals representative of the image are transmitted to thedisplay device 116 to provide a visual display of the image.Specifically, the MR signals fill or form a k-space which is Fouriertransformed to obtain a viewable image. More specifically, all of thedata points in a so-called “k-space” (i.e., frequency space) must becollected. The collection of data points is referred to herein as animage data set 81. The image data set 81, e.g. the processed signalsrepresentative of the image, are then transmitted to the display device116. In one embodiment, the image data set 81 may be stored in a memory,such as memory 114. Optionally, the image data set 81 may be stored inthe motion characterization module 78 or the controller 106, forexample. Moreover, although the motion characterization module 78 isshown as included in the PET system 13, a separate motioncharacterization module may also be used with the MRI system 15. In theexemplary embodiment, the imaging system 10 includes a single motioncharacterization module 78 that performs characterization on image datagenerated using any imaging modality associated with imaging system 10.

It should be noted that the various embodiments of the present inventionare not limited to use in connection with the MRI system 15 describedherein, but may be implemented in connection with other MRI systemsand/or other medical imaging systems. For example, in an MRI system 15as shown in FIG. 3, array 126 may be replaced with coil arrays 111.Further, and for example, instead of the electromagnet 102, asuper-conducting magnet configured having a cylindrical bore shape maybe used as part of an open MRI system having a vertical B_(o) field.

FIGS. 4A and 4B are simplified block diagrams of an exemplary method 150performed by the multi-modality imaging system 10 shown in FIG. 1 inaccordance with an embodiment of the present invention. In the exemplaryembodiment, the method 150 may be implemented using the motioncharacterization module 78. As discussed above, although the motioncharacterization module is illustrated as being embodied in the PETimaging system 14, it should be realized that the motioncharacterization module may be embodied as part of the multi-modalityimaging system 10, and/or may be used with any imaging system. In theexemplary embodiment, the method 150 identifies internal regions ofmotion within the object 16. After the regions of motion have beenidentified, a scanning protocol is selected based on the amount ofmotion detected in each region. For example, a first scanning protocolmay be used to scan internal regions having little or no motion such asthe head or upper torso. A second scanning protocol may be used to scanregions having an increased level of motion such as for example adiaphragm or lung area. The method 150 characterizes the real-timemotion for a plurality of anatomical regions within the object 16. Thecharacterization of the motion may include for example, the amount ofthe motion in a predetermined anatomical region of the object 16. Basedon this characterization, an appropriate scanning protocol is selectedfor each anatomical region to be scanned as discussed in more detailbelow. In the exemplary embodiment, the real-time motion determined foreach anatomical region is used to reduce imaging artifacts in regionsthat exhibit an increased level of motion. It should be realized thatalthough method 150 is described with respect to the emission data set80 obtained from the PET imaging system 14 in one embodiment, thatmethod 150 may be applied to a transmission data set obtained from theCT imaging system 12, data obtained from the MR system 15, or any otherimaging system, and that the emission data set 80 is exemplary only. At152, internal motion information of the object 16 is generated. In theexemplary embodiment, the object 16 is a person, however, the method 150may be applied to any other living or non-living object. In oneexemplary embodiment, the internal motion information of the object 16may be generated using the CT imaging system 12. For example, at 170 aCine-CT scan of the object 16 may be performed. A Cine-CT scan istypically utilized to acquire multiple CT images during a respiratorycycle. At 172, at least two of the low-dose images are utilized togenerate a difference image. This difference image may then be used togenerate the internal motion information. Optionally, a total MeanSquare Error may be used with the pre-existing Cine-CT data, over alltime-points, with respect to one of the time-points may be used.Optionally, the CT imaging system 12 may be used to perform a singlepre-scan, or a normal fast scan of the object 16. For example, the CTimaging system 12 may be operated in the helical mode to generate aplurality of images that are utilized to produce the difference image.In the exemplary embodiment, the plurality of images may be selectedbased on the respiratory cycle. For example, two scans may be performed,the first scan at inspiration and the second scan at expiration.Optionally, the plurality of images may be selected based on a motionsignal acquired from an external tracker. In the above embodiments,differences of images were computed to obtain motion information. Inanother embodiment, two or more images may be registered with eachother, the displacement vectors are the determined. Relatively largedisplacement vectors indicate relatively large amount of motion, whereasrelatively small displacement vectors indicate a relatively low amountof motion.

In another exemplary embodiment, the internal motion information of theobject 16 may be generated using the CT imaging system 12. For example,the internal motion information of the object 16 may be generated byperforming scout scans of the object 16. In the exemplary embodiment, atleast two CT scout scans are utilized to generate the motion informationfor various anatomical regions within the object 16. A scout scan istypically a scan performed by the CT imaging system 12 of a relativelyshort duration that produces a single image, similar to an x-ray, of theobject 16. Referring again to FIG. 4, at 154, a first scout scan ofobject 16 is performed. At 156, a second scout scan of object 16 isperformed. It should be realized that two scouts is exemplary, and thatmore than two scout scans may be performed to generate additional motioninformation or to further characterize the motion of the object. At 158,the data produced from the scout scans is then combined to produce adifference image, or Mean Square Error image. Optionally, registrationis used to determine the amount of motion.

In another exemplary embodiment, the internal motion information of theobject 16 may be generated using the MRI system 15. For example, at 174at least one low-resolution scan, or a navigator scan, of the object 16is performed using the MR imaging system 15. A “navigator” scan is animaging protocol wherein a (fast) MR scan is performed over a ID region(i.e. a line), for example a line orthogonal to the diaphragm. Becauseonly a small amount of space is covered, the navigator scan can beperformed very quickly to generate a plurality of ID snapshots byrepeating this acquisition. The operator may then observe how the“profile” changes with time (e.g. giving you information on the locationof the diaphragm over time).

The low-resolution scan may be acquired at a resolution lower than thescan of interest. A sequence of low-resolution MRI scans is effective ingenerating motion information for a relatively large region of theobject 16. In the exemplary embodiment, the MRI system 15 may also beutilized to characterize the motion of object 16 using several differentscanning procedures. For example, an MR proton-density weighted pulsesequence may be used to measure physical organ translation, rotation, ordeformation, a more sophisticated pulse sequence such as phase-contrastMR imaging may be used to measure tissue velocity, and DENSE MR imagingmay be used to measure organ stress and strain. It should be realizedthat each of the above described methods can produce real-time motioninformation of the object currently being imaged.

In the previous paragraphs, various ways were discussed to obtain animage that represents the amount of motion in various anatomical regionsof the object 16. For example, FIG. 5A is a graphical representation ofan exemplary motion image illustrating the motion characterization ofthe object 16 wherein the x-axis represents the range of the body, andthus the time and duration of the motion. The y-axis represents theamount of the motion. As shown in FIG. 5A, the motion image indicatesthat the internal motion within the object 16 is varying along thelength of the object 16.

Referring again to FIG. 4, at 180 the internal motion of the object 16is determined for a plurality of anatomical regions within the object 16using the difference information generated above. In the exemplaryembodiment, the difference image generated at 158, and shown in FIG. 5A,is used to describe the method of determining the internal motion. Inthe exemplary embodiment, by visual observation, the internal motion ofobject 16 is characterized by four regions of internal motion. Forexample, in the exemplary embodiment, the four separate motion regionsinclude a motion first region 160 which correlates to a first anatomicalregion 164, a second motion region 161 which correlates to a secondanatomical region 165, a third motion region 162 which correlates to athird anatomical region 166, and a fourth motion region 163 whichcorrelates to a fourth anatomical region 167. Assuming object 16represents a patient, the first anatomical region 164 represents theupper torso, the second anatomical region 165 represents the apex of thelungs to the base of lungs proximate to the diaphragm, the thirdanatomical region 166 represents the torso region downstream from thediaphragm, and the fourth anatomical region 167 represents the lowertorso. As shown in FIG. 5A, the second and third regions 161 and 162have increased motion when compared to first and fourth regions 160 and163. Accordingly, the second and third anatomical regions 165 and 166have increased motion when compared to the first and fourth anatomicalregions 164 and 167.

The internal motion of various regions within the object 17 isdetermined by mathematically analyzing the motion information. Forexample the amount and location of the motion are determined to identifythe motion characteristics of the various anatomical regions within theobject 16. In the exemplary embodiment, the amount of the motioninformation 182 is determined using the motion characterization module78, shown in FIG. 2, for example. As shown in FIG. 5A, the motioninformation 182 includes at least one portion 200 of the motioninformation that is greater than a first predetermined threshold 202. Inthe exemplary embodiment, the motion information 182 also includes asecond portion 204 of motion information that is greater than a secondpredetermined threshold 206.

To determine the motion within the object 16, the motion information isdivided into regions, such as regions 160-163 based on the displacementof the motion signal using the motion characterization module 78, forexample. More specifically, the motion information 182 is analyzed todetermine if/when the motion information 182 exceeds or falls below apredetermined threshold, such as a threshold 202. The motioncharacterization module 78 then may activate a flag for example, thatdefines the ending of one region and the beginning of another region.

More specifically, as shown in FIG. 5, the motion characterizationmodule 78 determines when the motion information 182 exceeds thepredetermined threshold 202. The motion characterization module 78 thenactivates a flag that defines the leading boundary of the second region161, and thus the ending boundary of the first region 160. When themotion information 182 falls below threshold 202 or optionally a lowerthreshold 206, the motion characterization module 78 activates anotherflag that defines the end of the second region 161. The flag alsodefines the beginning of another region, such as the third region 162.In the exemplary embodiment, the motion characterization module 78 maydefine a plurality of regions based on a plurality of predetermineddisplacement thresholds. The displacement and periodicity of the motioninformation 182 is determined for a second region of interest, such asthe third region 162, for example. In one embodiment, the first regionis adjacent to the second region. Optionally, the first region isseparated from the second region by a time t.

To determine the second region 162, the motion characterization module78 determines when the motion information 182 exceeds threshold 206 andactivates another flag that defines the beginning of the third region162 and/or the end of the second region 161. When the motion informationthen falls below the threshold 206, the motion characterization module78 activates another flag that defines the end of the third region 162and/or the beginning of the fourth region 163. It should be realizedthat in the exemplary embodiment, the motion information 182 may includea single portion that exceeds a predetermined threshold. In this case,the motion information is divided into a first region, a second regionwherein the threshold is exceeded, and a third region, wherein neitherthe first or third regions include motion information that exceeds thepredetermined threshold, such as first and fourth regions 160 and 163.

Referring again to FIG. 4, at 208 a scan protocol is selected for eachanatomical region, e.g. anatomical regions 164-167 based on thedetermined motion as describe above. As discussed above, each anatomicalregion 164-167 is defined based on the quantity of real-time motionwithin the respective anatomical region. Accordingly, a scan protocol isselected for each anatomical region based on the real-time motion withineach respective motion region. For example, first and fourth anatomicalregions 164 and 167, each having a low level of motion, may be scannedusing a first scan protocol. Whereas the second and third anatomicalregions 165 and 166 each have a larger amount of motion, and thus may bescanned with a second different scan protocol. Moreover, since themotion in the second anatomical region 165 is even larger when comparedto the motion in the third anatomical region 166, each of the second andthird anatomical regions 165 and 166 may be scanned using differentprotocols.

FIG. 4 illustrates a plurality of scan protocols. For example, FIG. 4illustrates six scan protocols 210-220 that may be selected and/ormodified based on the determined displacement and/or periodicity of themotion in the predefined anatomical regions 164-167. In the exemplaryembodiment, another scanning protocol may be selected to scan the secondand third anatomical regions 165 and 166 and another different scanningprotocol is used to scan the first and fourth anatomical regions 164 and167. The different scanning protocols include for example, modifying theduration of a scan acquisition, modifying a detector configuration,modifying the quantity of gates used to collect the imaging data,modifying an MR pulse sequence, modifying the sequence of bed positions,and/or modifying the type of scan acquisition.

For example, at 210 a scan protocol may be selected that modifies theduration of the scan acquisition procedure based on the motion within aregion. For example, referring again to FIG. 5B, and as discussed above,the first and fourth anatomical regions 164 and 167 each have arelatively low level of motion. Accordingly the first and fourthanatomical regions 164 and 167 may be scanned for a first scan duration.Modifying the duration of the scan may be implemented by selecting atable speed for each region. For example, since the first and fourthanatomical regions 164 and 167 have a relatively low quantity of motion,the table speed may be set to a first scan speed 230. Moreover, sincethe second anatomical region 165 has a larger amount of motion, comparedto the first and fourth anatomical regions 164 and 167, the table speedmay be set to a second scan speed 232 different than the first scanspeed 230. In the exemplary embodiment, the second scan speed 232 isslower than the first scan speed 230 such that more information isacquired in the second anatomical region 165 than is acquired in thefirst anatomical region 167. The increased quantity of informationfacilitates improving reducing imaging artifacts in the final image.Moreover, the third anatomical region 166 has a larger amount of motionthan the first anatomical region 164, but less motion than secondanatomical region 165, the table speed may be set to a third scan speed234. In the exemplary embodiment, the third scan speed 234 is slowerthan the second scan speed 232, and is faster than the first scan speed230 such that less information is acquired than in the third anatomicalregion 166 than the second anatomical region 165, but more informationthan is acquired from the first anatomical region 164. It should berealized that the object 16 may be divided into numerous regions, eachscanned at differing scan speeds. Optionally, for example when a PETimaging system is utilized, the scanning protocol is modified such thatthe duration of the scan is increased for regions of greater motion anddecreased for regions having less motion.

Referring again to FIG. 4, at 212 a scanning protocol may be selected toassociate a predetermined quantity of data bins to each anatomicalregion. During operation, data bins are utilized by the imaging systemto reduce the effect of motion on image quality. For example, reducingthe table speed and/or increasing the scan duration increases thequantity of information collected in the region being scanned. As aresult, the increased scanning information may be gated to an increasedquantity of bins to increase the resolution in this region. Optionally,as opposed to using more bins, a single bin may be used and the fractionof time over the whole cycle that corresponds to this bin may be reducedto “freeze” the motion in a single image. Having more bins would achievethe same effect, but would also lead to more images.

More specifically, referring again to FIG. 5C, the first anatomicalregion 164 has relatively little motion. Accordingly, the informationobtained during the scanning operation may be gated to a single bin 240.Moreover, the second anatomical region 165 has an increased quantity ofmotion. As discussed above, the second anatomical region 165 may bescanned at a slower scanning speed to generate an increased quantity ofinformation. In the exemplary embodiment, the scan protocol controllingbin quantity for the second anatomical region 165 is modified to providean increased quantity of bins 242 that are potentially configured toreceive the increased quantity of motion information obtained during theslower scanning procedure. Accordingly, the scan protocol may bemodified such that the third anatomical region 166 has more bins 244than the first anatomical region 164, but fewer bins than the secondanatomical region 165, etc. In this manner, the effects of motion ofimage quality may be reduced for each anatomical region based on thedetermined motion within the respective anatomical region.

At 214, a scanning protocol may be selected or modified to adjust thesequence of bed positions during the scanning operation. For example,the bed 214, shown in FIG. 1, may be positioned to scan the first andfourth regions 160, 163 at a first speed and using a first quantity ofgates and then scan the second and third regions 161, 162 at a secondspeed and using a second quantity of gates.

At 216, a scanning protocol may be selected to modify the detectorconfiguration. For example, the detector configuration may be modifiedto enhance the image resolution in certain areas based on the determinedmotion in the area.

At 218, a scanning protocol may be selected to set the MR pulsesequence. For example, in 2D multi slice MR imaging, the number ofacquisitions can be changed on a slice by slice basis depending on theamount of motion measured. Slices in one region having more motion canbe acquired with multiple acquisitions and averaged together to reducemotion artifacts, whereas slices in another region having lower motioncan be acquired with fewer acquisitions.

At 220, a scanning protocol may be selected to set the scan acquisitiontype. For example, for CT, regions without motion above a certainthreshold could be covered with a (fast) helical CT, while in regionswith motion, a CINE CT can be used such that different stages of themotion can be captured. This would for example by useful when the CT islater used for attenuation correction of a PET or SPECT scan.

During operation, at 222, the first region of the object 16 is scanned.For example, the first anatomical region 164 is scanned using a firstscan protocol as discussed above. In the exemplary embodiment, at 224the second anatomical region 165 is scanned using a second differentscan protocol. As discussed above, the scan protocols are selected basedon the quantity of internal motion in each anatomical region beingscanned. As a result, the scan protocols are also selected based on thedetermined motion in each anatomical region, e.g. regions 164-176. Forexample, since the first anatomical region 164 has a first quantity ofmotion and the second anatomical region 165 has a different quantity ofmotion, the first and second anatomical regions 164 and 165 are scannedusing different scan protocols. The scanning information is then gatedto separate bins as described above. At 226, an image of the object 16is generated using the information generated using the scanningprotocols described above.

In the exemplary embodiment, the above described methods of determiningthe internal motion of the object 16 may be used separately or incombination. Optionally, the above described methods may be used inconjunction with pre-existing information to improve or enhance thecharacterization of the motion data determined above. The pre-existingmotion data may be combined with the scout scan images described aboveto improve the motion determination. For example, assuming that SPECT/CTor PET/CT system is utilized, pre-existing CT scans or Cine-CT scans maybe correlated with the real-time motion information to improve themotion determination. In another option, gated dated from a previousscan of the same patient may be used to determine regions of motionduring a current examination procedure. In another option, a databaseincluding motion information acquired during a previous examination maybe used to determine regions of motion during the current examinationprocedure. For example, real-time motion information may be determinedas discussed above and then compared to motion information stored in adatabase of the same patient, or another patient, to find closestmatching motion information in the database. It should be realized thatthe above examples of preexisting motion data are exemplary and thatother pre-existing information may be used to improve the quality of thereal-time motion information.

A technical effect of method 150 is to increase image quality bydetermining patient motion. More specifically, patient motionsignificantly degrades image quality in medical imaging. The method andapparatus described herein provide a fully automatic method of reducingmotion-related imaging artifacts by determining the quantity of motionin at least one region of an object being imaged. A scanning protocol isthen adapted or determined based on the quantity of determined motion ineach region. As a result, the image generated using the different scanprotocols has less artifacts than known imaging methods. Morespecifically, the method and apparatus described herein identify andcharacterize involuntary motion such as cardiac or respiratory motion. Afirst acquisition protocol for regions where there is large motion (e.g.around the diaphragm) is then utilized. A second acquisition protocol isutilized for regions having less motion. For example, regions havinglittle motion utilize one protocol, e.g. ungated, whereas regions havingmore motion use a second protocol, e.g. longer acquisition time or moreor shorter gates. In the exemplary embodiment, the system describedherein is operating in a coupled manner. More specifically, the methodand apparatus described herein increase image quality by substantiallycontinuously acquiring motion information, analyzing the motioninformation, and then refining the imaging parameters based on themotion information. In this manner, the system continuously refines andadjusts the imaging parameters to improve image quality.

Some embodiments of the present invention provide a machine-readablemedium or media having instructions recorded thereon for a processor orcomputer to operate an imaging apparatus to perform an embodiment of amethod described herein. The medium or media may be any type of CD-ROM,DVD, floppy disk, hard disk, optical disk, flash RAM drive, or othertype of computer-readable medium or a combination thereof.

The various embodiments and/or components, for example, the monitor ordisplay, or components and controllers therein, also may be implementedas part of one or more computers or processors. The computer orprocessor may include a computing device, an input device, a displayunit and an interface, for example, for accessing the Internet. Thecomputer or processor may include a microprocessor. The microprocessormay be connected to a communication bus. The computer or processor mayalso include a memory. The memory may include Random Access Memory (RAM)and Read Only Memory (ROM). The computer or processor further mayinclude a storage device, which may be a hard disk drive or a removablestorage drive such as a floppy disk drive, optical disk drive, and thelike. The storage device may also be other similar means for loadingcomputer programs or other instructions into the computer or processor.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. For example, the ordering of stepsrecited in a method need not be performed in a particular order unlessexplicitly stated or implicitly required (e.g., one step requires theresults or a product of a previous step to be available). While thedimensions and types of materials described herein are intended todefine the parameters of the invention, they are by no means limitingand are exemplary embodiments. Many other embodiments will be apparentto those of skill in the art upon reviewing and understanding the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein.”Moreover, in the following claims, the terms “first,” “second,” and“third,” etc. are used merely as labels, and are not intended to imposenumerical requirements on their objects. Further, the limitations of thefollowing claims are not written in means-plus-function format and arenot intended to be interpreted based on 35 U.S.C. §112, sixth paragraph,unless and until such claim limitations expressly use the phrase “meansfor” followed by a statement of function void of further structure.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method for reducing, in an image, motion related imaging artifacts,said method comprising: automatically determining an amount of motionfor a first region and a second region of the object, each region havinga different level of motion; automatically determining if the amount ofmotion for the first or second region exceeds a predetermined motionthreshold; scanning the first region using a first gated scan protocolwhen the amount of motion in the first region is greater than thepredetermined motion threshold, the first gated scanning protocol havinga first quantity of gates; re-scanning the second region using at leastone of a second different gated scanning protocol having fewer gatesthan the first scanning protocol and an ungated scanning protocol whenthe amount of motion in the second region is less than the amount ofmotion in the first region; and generating an image of the object basedon the first and second regions.
 2. The method in accordance with claim1 further comprising determining the amount of motion of the two regionsusing at least one of a mean square error image generated from at leasttwo images and motion vectors obtained from registering at least twoimages.
 3. The method in accordance with claim 2 wherein determining theamount of motion further comprises registering at least two imagesacquired from two different imaging modalities, the two images includingan x-ray image, an ultrasound image, a CT image, a CT scout scan image,and a low-resolution MR image.
 4. The method in accordance with claim 2wherein determining further comprises determining the amount of motionof the two regions using image data generated from a Cine-CT scan. 5.The method in accordance with claim 2 wherein determining furthercomprises determining the amount of motion of the two regions using atleast one of a DENSE MR imaging technique and a phase-contrast MRimaging technique.
 6. The method in accordance with claim 2 whereindetermining further comprises determining the amount of motion of thetwo regions using image data generated from at least one of a PET gatedscan, a SPECT gated scan, a CT gated scan and a MR gated scan.
 7. Themethod in accordance with claim 1 further comprising modifying at leastone of the first and second scan protocols when the internal motion ofat least one of the regions exceeds the predetermined motion threshold.8. The method in accordance with claim 1 wherein scanning the secondregion further comprises modifying the second scan protocol to increasea scan acquisition duration of the second region when the second regionhas greater motion than the first region.
 9. A method in accordance withclaim 1 wherein scanning the second region further comprises modifyingthe second scan protocol to decrease table speed when the second regionhas greater motion than the first region.
 10. A multi-modality imagingsystem comprising a first modality unit, a second modality unit, and acomputer operationally coupled to the first and second modality units,wherein the computer is programmed to: automatically determine an amountof motion for a first region and a second region of the object, eachregion having a different level of motion; automatically determine ifthe amount of motion for the first or second region exceeds apredetermined motion threshold; scan the first region using a firstgated scan protocol when the amount of motion in the first region isgreater than the predetermined motion threshold, the first gatedscanning protocol haying a first quantity of gates; re-scan the secondregion using at least one of a second different gated scanning protocolhaving fewer gates than the first scanning protocol and an ungatedscanning protocol when the amount of motion in the second region is lessthan the amount of motion in the first region; and generate an image ofthe object based on the first and second regions.
 11. The multi-modalityimaging system in accordance with claim 10, wherein the first modalitycomprises a computed tomography imaging system and the second modalitycomprises a Positron Emission Tomography system.
 12. The multi-modalityimaging system in accordance with claim 10, wherein the computer isfurther programmed to determine the amount of motion of the two regionsusing at least one of a mean square error image generated from at leasttwo images and motion vectors obtained from registering at least twoimages.
 13. The multi-modality imaging system in accordance with claim10, wherein the computer is further programmed to modify at least one ofthe first and second scan protocols when the amount of motion of atleast one of the regions exceeds a the predetermined threshold.
 14. Themulti-modality imaging system in accordance with claim 10, wherein thecomputer is further programmed to determine an amount of motion for eachregion of the object and modify at least one of the first and secondscan protocols based on the determined amount of motion.
 15. Themulti-modality imaging system in accordance with claim 10, wherein thecomputer is further programmed to modify the second scan protocol toincrease a scan acquisition duration of the second region when thesecond region has greater motion than the first region.
 16. Themulti-modality imaging system in accordance with claim 10, wherein thefirst modality comprises a Magnetic Resonance Imaging system and thesecond modality comprises at least one of a Positron Emission Tomographysystem and an X-ray system.
 17. The multi-modality imaging system inaccordance with claim 10, wherein the computer is further programmed toestimate the internal motion of the two regions based on at least one ofa priori knowledge and a comparison of a scout scan with an atlas.
 18. Anon-transitory computer readable medium encoded with a programprogrammed to instruct a computer to: automatically determine an amountof motion for a first region and a second region of the object, eachregion having a different level of motion; automatically determine ifthe amount of motion for the first or second region exceeds apredetermined motion threshold; scan the first region using a firstgated scan protocol when the amount of motion in the first region isgreater than the predetermined motion threshold, the first gatedscanning protocol haying a first quantity of gates; re-scan the secondregion using at least one of a second different gated scanning protocolhaving fewer gates than the first scanning protocol and an ungatedscanning protocol when the amount of motion in the second region is lessthan the amount of motion in the first region; and generate an image ofthe object based on the first and second regions.
 19. The non-transitorycomputer readable medium in accordance with claim 18 wherein the programis programmed to further instruct a computer to determine the amount ofmotion of the two regions using a difference image generated from atleast two scout scans.
 20. The non-transitory computer readable mediumin accordance with claim 18 wherein the program is programmed to furtherinstruct a computer to modify at least one of the first and second scanprotocols when the amount of motion of at least one of the regionsexceeds the predetermined threshold.
 21. The non-transitory computerreadable medium in accordance with claim 18 wherein the program isprogrammed to further instruct a computer to determine the amount ofmotion for each region of the object and modify at least one of thefirst and second scan protocols based on the determined amount ofmotion.